Joining flat cable or ribbon cable to connectors can be accomplished by a number of different methods, with soldering being probably the most reliable. However, if all the solder terminations must be done by hand, the costs involved and the time required to perform a multiplicity of repetitive soldering operations far outweigh any gains in reliability. In addition, as connector pin spacing decreases, due to higher interconnection densities, the reliability of hand soldering decreases because of the possibility of solder bridging terminations and shorting out adjacent connectors. It would therefore be desirable to have a solder system in which all leads can be soldered to the connector simultaneously, rapidly and reliably for a wide range of a number of terminations and spacings.
In the past, various systems have been developed for simultaneously applying a plurality of bodies of solder. One such system is that disclosed in U.S. Pat. No. 3,396,894, which discloses the prepackaging of metered amounts of flux and solder in a heat-recoverable preformed polymer sheet which forces the solder into place. The patent teaches the use of discrete pieces of solder which must be precisely positioned above regions to be soldered. As heat is applied, the polymer sheet returns to its original flat configuration prior to solder melting.
U.S. Pat. No. 3,719,981 discloses an alternative method of applying solder balls, which are appropriately spaced on the tacky surface of a pressure-sensitive tape, to solder bumps used for connections.
Both of the above methods rely on the positioning of the small pieces of solder immediately adjacent to the terminals which are to be soldered, and, because small pieces of solder are used, each of the solder systems disclosed is difficult to manufacture.
U.S. Pat. No. 3,750,252 discloses the use of a single continuous piece of solder to simultaneously solder a large number of terminals. The solder wire extends along a terminal strip and, on heating, the solder melts and coalesces on the individual contacts to form independent connections.
U.S. patent application Ser. No. 133,038, filed Mar. 24, 1980 now abandoned and assigned to the assignee of the present invention, also describes the use of a continuous solder strip. In this application, the disclosure of which is incorporated herein by reference, the solder strip is embedded within a heat-recoverable polymeric strip which, together with interfacial forces (capillary action), acts to direct the solder towards individual contacts when it melts.
With the increasing use of ribbon or "flexprint" cable, especially multilayer cable, which is analogous to flexible printed circuit board, and the decreasing size of many electronic assemblies, so that bulky connectors are disadvantageous, a method of terminating flat cables to flat substrates has also become extremely desirable.